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Chitin synthases PcCHS and PsCHS1 are involved in sporangial development, zoospore production, and plant infection in Phytophthora

Xili Liu: China Agricultural University

<div>Oomycetes exhibit a filamentous growth morphology that is very similar to that of many fungi, but they are not fungi or even not related to fungi. A low content or lack of chitin in oomycetes cell walls has been taken as a criterion for that differentiates them from true fungi. <em>Phytophthora capsici</em> and<em> P. sojae </em>are both representative oomycetes species and have a worldwide distribution. Interestingly, no chitin was detected in <em>Phytophthora</em> cell walls, but putative chitin synthase genes are presented in <em>Phytophthora</em> species. In this study, we identified a <em>CHS</em> gene named <em>PcCHS</em> from <em>P. capsici</em>, and a <em>CHS</em> genes named <em>PsCHS1 </em>from <em>P. sojae</em>. The transcript patterns of <em>PcCHS</em> and <em>PsCHS1</em> were similar in different stages; both of them had higher expression level in zoospores, cysts and infection stages. By systematic characterization of the impact of individual gene knockout, silencing, and overexpression on asexual and sexual growth, cell wall composition, chemical sensitivity, and virulence on plants, it showed that <em>PcCHS</em> and<em> PsCHS1 </em>were mainly involved in sporangial development, zoospore release and pathogenicity on plants. In addition, PsCHS1-GFP fluorescence was concentrated in brightly fluorescent cell membrane in the sporangia and hyphae with some diffuse fluorescence in the cytoplasm. Thus, our results suggest that <em>PcCHS </em>and<em> PsCHS1 </em>are not involved in chitin biosynthesis, but required for the asexual growth and plant infection in <em>Phytophthora</em>.</div>